Metallic implants can cause substantial image artifacts in magnetic resonance imaging (MRI). Susceptibility variations between metal and surrounding tissue cause significant localized variations in the static magnetic field. These magnetic field variations then cause large resonant frequency variations and significant dephasing of the signal. These effects result in MRI imaging artifacts near the metal, including signal loss, failure of fat suppression, geometric distortion, and bright pile-up artifacts.
Existing multi-spectral imaging (MSI) techniques significantly reduce metal-induced artifacts, but often suffer from residual artifacts in the vicinity of metal due to strong metal-induced off-resonance gradients interfering with the frequency-encoding gradients. These residual artifacts resulting from the limitation of frequency encoding appear as intensity variations, including hyper-intensities (pile-ups) and signal fluctuations (ripples), and may also cause loss of image resolution.
Fully phase-encoded methods can overcome this limitation, but they usually incur prohibitively long scan times. Other existing techniques, including Jacobian-based intensity correction, slice overlap, and deblurring, can reduce the appearance of intensity fluctuations. However, these techniques cannot recover the lost structural information in areas where the off-resonance gradient cancels the frequency-encoding gradient.